Making gasoline



- J. c. MUNDAY MAKING GASOLINE Filed July 6, 1944 April 23, 1946.

v2 Odo duomium Juan ,0! 3

w uobaimw John C. mundaz Unverzbcr e n r o b b Patented Apr. 23. 1946John C. Munday,

Cranford, N. J., assignor to Standard Oil Development Company, acorporation of Delaware Application July 6, 1944, Serial No. 543,626

Claims.

The present invention relates to an improved process for the productionof gasoline and other light hydrocarbons from heavier hydrocarbon oilsby catalytic cracking.

The catalytic cracking of hydrocarbon oils,

, such as gas oil, to form cracked gasoline has now become commonpractice in the petroleum refining industry, While the raw rackedgasoline has, of course, many advantages over the gasoline produced bythe older thermal cracking methods, nevertheless it has to undergoconsiderable after-treatment and/or refining in order to produce finallya satisfactory commercial product. In general, there are two mainconsiderations presented to the refinery in after-treating or handlingthe material recovered from a cracking reactor or zone. In the firstplace, the raw product is not 100. per cent gasoline and containssustantial quantities of unconverted ga oil or heavier ends which,during cracking, have undergone some change which makes them lessdesirable for recracking than the original feed stock. Thus theunconverted gas oil commonly called cycle oil," since it is returned orrecycled in whole or in part to the cracking zone, acquires as a resultof the operation high molecular-weight aromatics containing two or morebenzene rings in a condensed nucleus. The presence of these aromatics isdetrimental to the operation of cracking, since they decompose duringthe cracking orrecracking to .form unduly large quantities of so-calledcoke, a carbonaceous deposit which forms on. the catalyst. Consequently,

'it is desirable to treat this cycle oil to improveits qualities beforecracking.

Withrespect to the gasoline itself, particularly where the object of theprocess is to produce aviation gasoline, the same invariably containssubstantial quantities of normally liquid olefinic hydrocarbons which.are undesirable particularly when the gasoline is eventually to beblended it is againsubjected to .with lead tetraethyl, since such anolefin-containing gasoline is less responsive to octane numberimprovement by the addition of lead tetraethyl than a, saturatedmaterial would be. In other words, such a gasoline fraction is said tohave a lower lead susceptibility (a technical term in this particularart) having the significance indicated.

The main object of the present invention is to gasoline so as torenderit more suitable for re-- treatment in a cracking zone.

A secondary object of my invention is to improve gasoline fractions andthe cycle oil in the absence of a fraction boiling between the gasolineand the initial feed stock in order to im: prove the economics of theoverall process, in particular to effect the saving in hydrogen which isone of the materials I employ in my process.

A third object of the present invention is to improve the quality ofboth the gasoline and the cycle oil recovered from a catalytic crackingoperation in a more expeditious and economical manner than has beenpossible heretofore.

Other and further objects of the present invention will appear from thefollowing more detailed description and claims.

In the accompanying drawing, I have shown diagrammatically merely theessential apparatus of a unit in which a preferred modification of myinvention may be carried into practical effect,

f with only so much of the accessory apparatus as improve the normallyliquid cracked portions of a cracked gasoline and, at the same time, toimprove the so-called cycle oil or that portion of the original feedstock which is not converted to is necessary to aiiord a clearunderstanding of the invention.

Referring in detail tolthe drawing, a gas oil,

which may be a West Texas crude oil boiling in the range of from 500 F.to 800 F. and having an A. P. I. gravity of about 30, is introduced intothe system through line I, thence heated in a fired coil 3, or othersuitable means, to a temperature of, say, 900 F., whereupon it isWithdrawn through line 5 and discharged into a cracking vessel l0containing a catalyst C. The pressure employed in the cracking operationmay be atmospheric or thereabouts, for example in the range 0 to lbs.per square inch gauge. The catalyst may be a natural or acid-treatedbentonitic clay, or a synthetic gel of silica and alumina. In themodification of my invention which I have shown to illustrate myinvention, the cracking is carried out in a stationary bed type ofcatalyst contained in a cylindrical or other suitable case l0. Sincecokeis formed on the catalyst during cracking, it is generally desirableto provide more than one catalyst case so that by proper alternation theoil flow can be made continuous even while coke is being removed byperiodic burning with air. It should be appreciated that I may carry outmy process of cracking in any of the known methods; such as theso-called fluid catalyst type of operation where the catalyst inpowdered condition is passed through a so-called delayed settler type ofreaction and regeneration zones, in the form of a fluidized mass ofcatalyst admixed with reaction and regeneration vapors,

7 detail the cracking process.

or I may use other known types of operation where the catalyst in theform of grains, granules lumps. and the like, moves by gravity or forcedcirculation through a reaction zone and a regeneration zone. However,since the gist of my invention resides in thesubsequent treatment of thecrackedproduct rather than in a specific type of cracking, it will notbe necessary to describe in Cracked products from the illustration Ihave shown are withdrawn from the reactor through a line l2 andimmediately discharged into a fractional distillation zone M where thecrude cracked products are fractionated into the following fractions:First, there is taken overhead through line It that portion of the totalproduct which includes the lighter fractions up to the C5 hydr0carbons.-This material is passed through cooler l6 into separator ll; light gasesare removed overhead from the separator through line It and liquidhydrocarbons, including C4 and some C3, are removed through line I9 andmay be utilized in alkylation and polymerization processes. A secondfraction comprising the CIR-325 F. hydrocarbons is withdrawn throughline 22, and acycle oil fraction boiling above about 500 F. or 550 F. iswithdrawn through line 24, These two fractions are combined and it iswith respect to the refining of these particular said fractions that myinvention is principally concerned. In treating these fractions, I firstpass them by means of a pump (not shown) through line 22 and through aheating means, such as fired coil 30, and thence through line 32 andthen into a hydrogenation reactor 40. Simultaneously, hy-

drogen from some source is passed from line 50 through a suitableheating means 55, which may be afired coil, and thence discharged vialine 56 into line 32 where it admixes with the heated hydrocarbons andis discharged with the latter into the'hydrogenation reactor 40. Thehydrogen employed is preferably that produced in the cracking step,separated from cracked products in separator i1 and passed through linel8 into line 50.

In the hydrogenation reactor, the desired result is to saturate theolefins in the (Is-325 F. fraction of the gasoline withdrawn fromfractionating column I4, and at the same time to hydrogenate thearomatics, particularly the high molecular weight aromatics having twoor more benzene rings in a condensed nucleus, which are contained in theheavy bottoms withdrawn from fractionating column 14 through line 24. Toaccomplish this end, I maintain the following conditions in hydrogenator40:

Temperature 600 F. to 800 F. Pressure 200 lbs. to 3000 lbs.

. per sq. in. auge Oil feed rate 1 to 5 v./v./hr. Hydrogen, cu. ft.

per barrel feed 1000 to 6000 Under the conditions I have set forth inthe are group VI and VIII metals and metallic oxides,

such as nickel or molybdenum oxide or chromium oxide. The catalyst isalso preferably supported asoaaec does not deactivate the catalyst. Theoxidized catalyst maybe treated with hydrogen before placing it back onstream, if desired.

The treated materials are withdrawn from hydrogenator 40 through line80, thence discharged into a hydrogen separator 62 from which thehydrogen may be withdrawn through line 55 and recycled to line 50 forfurther use in the process. It may be and often is desirable to pass thehydrogen-containing gas in line 50 through a scrubber where it contactsin countercurrent flow an absorption oil, such as, say, a light naphthawhich scrubs out and/or dissolves light hydrocarbons thereby enrichingthe raflinate in hydrogen content. The bottoms withdrawn from separator62 through line 10 carrying a pressure reducing valve 13 are thendischarged into a fractionator 15 from which the now saturated Cs-325,F.gasoline fraction is withdrawn through line and delivered to storagedrum 8!.

. The bottoms from fractionator I5 are withdrawn through line 83, andthis material which is the cycle oil previously mentioned, improvedas'to its cracking properties, is discharged into feed inlet line I forfurther treatment in the cracker i0. The normally gaseous hydrocarbonsand possibly some hydrogen which are contained in the crude productwithdrawn from 40 are withdrawn overhead from fractionator 15 throughline and these may be disposed of in any convenient manner.

Of course, it will be understood that the raw gasoline collected instorage 8| may be corrected as to volatility by the additionof suitableblending agents thereto, or bythe removal of light ends and of coursemay be blended with up to 4 cc. of

to standard practice.

The cycle oil fraction which is subjected to mild hydrogenation has aninitial boiling point above about 500 F. or 550 F., and in a preferredoperation has a boiling range similarto that of the fresh feedstock. Ifthe aviation gasoline fraction, which is hydrogenated along with thecycle oil, boils up to 325 F. as mentioned above, it will contain the Caaromatics, the xylenes and ethyl benzene. In some cases, for examplewhen the capacity of the hydrogenation unit or the amount of hydrogenavailable is limited, it may be desirable to bypass the C8 aromaticfraction boiling between 265 F. and 325". F. around the hydrogenationstep, by passing it from fractionator I4 through line 82 to line 80 andthence to storage drum 8|. If the toluene concentration is high, it maybe desirable to bypass the 221 F.-325 F. fraction through line 82.

An intermediate fraction boiling between the cycle oil and the aviationgasoline, in example between 325 F. and 550 F., is withdrawn fromfractionator l4 and is rejected from the system, whereas by mildhydrogenation the aviation gasoline is improved in quality and the cycleoil is made more amenable toward cracking to high quality gasoline.Hydrogenation of the intermediate fraction is imdesirable since itsquality as a motor fuel is degraded by hydrogenation, and its value as acracking stock even after hydrogenation is far less than that of cycleoil or fresh feed. Rejection of the intermediate fraction therefore hasthe eiiect of increasing the overall quality of the aviation gasolineproduced and of plant capacity, and also of keeping hydrogen consumptionin line with hydrogen production in the cracking step.

Hydrogen consumption may also be decreased by bypassing the Ca fractionof the cracked products around the hydrogenation zone, by passing itfrom fractionator ll through lines 84 and 80 into storage drum 8 I Forexample, a Southwest Louisiana wide-cut gas oil having an A. P. I.gravity of 32, an aniline point of 1'75, and a boiling rangecorrespondingto per cent at 484, 50 per cent at 622, and an end point of700 F. is cracked at 975 F. employing a powdered silica-alumina catalystin 13:1 catalyst to oil weight ratio and a weight-space velocity of 4.On a volume per cent fresh feed basis, there are obtained 28 per centaviation gasoline of 7 lbs. vapor pressure which has an acid heat of a141 E, a bromine number of 74, and a boiling range of 110 F. to 332 F.,and 26 per cent cycle oil boiling above 500 F. The intermediate fractionwhich has a low octane number (65-70 C. F. R. Motor method) is rejectedfrom the process.

The aviation gasoline is fractionated into a light fraction and aheavier fraction boiling above 221 F. which contains xylenes and a smallamount of toluene. The heavier fraction is bypassed around thehydrogenation step. The light aviation fraction-and the cycle oilfraction are combined and are hydrogenated at 730 F., 3000 lbs. persquare inch pressure, 6000 cubic feet of hydrogen per barrel, and 1.0v/v./hr. space velocity, employing tungsten sulfide catalyst.

The hydrogenation product is fractionated, the light fraction iscombined with the bypassed aromatic fraction, and the heavierhydrogenated fraction is recycled to the cracking step. The

- oil feed, while increasing coke formation from 4.2

to only 5.0 weight per cent based on feed. Numerous modifications of myinvention failing within'the scope thereof may be made by 'thosefamiliar with this art.

What I claim is: 4

1. In the refining of the total products of a I catalytically crackedgas oil. the improvement which comprises withdrawing the product from acatalytic cracking zone, fractionally distilling the same into afraction consisting of- C5 hydrocarbons to those boiling up to about 325F. and a second fraction comprising the hydrocarbons 1 boiling aboveabout 500 R, combining the segrecombined fractions comprise an aviationgasoline having an aviation octane number of 96.5 by the AFB-1C methodas compared to 92 for the original cracked aviation gasoline, each beingtested at '7 lbs. vapor pressure with 4 cc. lead tetraethyl per gallon.

Recycle of the heavy hydrogenated cycle oil to the crackingstepincreases the yield of aviation gasoline from 28 to 37.3 per centbased on gas gated fractions, subjecting the combined fractions to amild catalytic hydrogenation in the presence of added hydrogen whereinthe oleiins are saturated andthe aromatics in the fraction boiling aboveabout 500 F. are substantially converted to naphthenes, in ahydrogenation zone,

withdrawing the hydrogenated products from the hydrogenation zone,fractionally distilling the hydrogenated products to recover a saturatedaviation gasoline boiling up to 325 F., separately r'ecoveringa fractionboiling above 500 F., and recycling'the last-named fraction to thecracking zone. 2. The method of claim 1 in which the hydrogenation iscarried out in the presence of a regenerable catalyst.

3. In the production of high quality aviation gasoline,the steps ofcatalytically cracking a gas oil, in a cracking zone, withdrawing thecracked products and fractionally distilling the same into non-aromaticand aromatic fractions boiling in the aviation gasoline range, and aheavy cycle oil fraction, combining the non-aromatic aviation gasolinefraction with the said heavy cycle oil fraction, subjecting the mixtureto a mild catalytic hydrogenation, separating the hydrogenated productsinto an aviation gasoline fraction and a- 5. The method of claim 3 inwhich the heavy,

recycle oil boils above about 500 F.

Joan c. MUNDAY.

